1. Field of the Invention
This invention relates to cable television communication systems. More particularly, this invention relates to a cable television system's return display unit (RDU), more specifically a unit which monitors the cable television system's return system to allow for activation and maintenance of the return system and to troubleshoot ingress, noise, "babbling box" problems from converters and modems and flatness of response.
2. Description of Related Art
Systems utilizing cable television have grown in importance and use over the years. Such systems employ coaxial cables, which provide excellent shielding from electromagnetic interference and radio frequency interference, to transmit television signals and other electronics communications signals to receivers. Originally, cable transmission was used in locations that could not receive broadcast transmissions directly because of distance or because of interfering buildings or terrain. In recent years, cable transmissions have become popular even in areas where reception of broadcasted television signals is satisfactory. In these areas, cable transmission provides additional channels and new services which were not available from broadcast television stations and provides programs with enriched content.
Cable television operates where a cable television (CATV) signal distribution system collects television and other electronic communications signals from various sources. Examples of such sources are a satellite receiving station, large antennas for off-the-air transmissions, or a signal directly from a locally generating source by telephone line, cable, microwave, etc. These signals are collected at a head end where they are processed and placed in a form which will be retransmitted to the various subscribers. A head end is the control center of a cable television system, where incoming signals are amplified, converted, and routed to subscribers through trunk and feeder paths of the system. Coaxial cables are used to connect bridge and line amplifiers to subscriber taps. Coaxial cables may be used for the trunk lines, as well as hybric fiber coaxial cables (HFC cables) and fiber optic lines, both of which provide for better transmission. To compensate for the amplitude loss of the combined television signals in the cables, amplifiers are located at spaced intervals along the cables. Amplifiers compensate for the drop in power level due to losses in the CATV system and due to the splitting which occurs as a cable signal progresses from the head end towards the subscribers. Amplifiers increase the magnitude of input signals to a prescribed operating parameter. The distribution network between the head end and the attached user devices also includes splitters, directional couplers, and taps that direct signal flow along desired paths. Filters that process signals depending on their frequency, and outlets that connect devices to the network.
Bidirectional CATV systems have become increasingly popular and supply customers with additional services, such as data communications and interactive videotext. To achieve bidirectional signal distribution, basic approaches can be employed.
One approach involves two-way communications over a single coaxial cable, with different frequency bands carrying signals in opposite directions.
Another approach to obtain bidirectional signal distribution involves two-way communications over dual coaxial cables, with each cable carrying signals in one direction.
Two-way communications can be implemented on a single coaxial cable by dividing the available frequency spectrum on the cable into two bands. These bands carry signals in opposite directions, called forward or downstream (away from the head end) and return, reverse or upstream (toward the head end). Devices attached to the network transmit to the head end on the return band, and receive from the head end on the forward band.
Two-way communications can also be implemented on two-way dual cable systems using two coaxial cables laid side-by-side. One cable provides the inbound (return) path signals to the head end. The second cable provides the outbound (forward) path signals from the head end to the attached devices.
In these 2-way cable television systems, various methods have been used to monitor the return system for numerous problems and performance measures, such as ingress, noise, "babbling box," converter problems and flatness of response. In the past when system problems arise, a service technician must go on-site to determine the source of the malfunction. This prior art method of determining the source of a malfunction is a time-consuming and difficult task.
The current state of art for monitoring the performance of return signals includes a spectrum analyzer/camera set up. A spectrum analyzer is a device which sweeps over a portion of the radio-frequency spectrum, responds to signals whose frequencies lie within the swept band, and displays them in relative magnitude and frequency on a cathode-ray-tube (CRT) screen. The system is typically set up for the 5-40 MHz spectrum. A video camera, placed above the CRT screen of the spectrum analyzer, transforms an optical display of the CRT screen into a video output. The output of the camera is modulated onto an open CATV channel on the system thru a standard CATV modulator. This system enables maintenance technicians to monitor the return system for problems or malfunctions. A spectrum analyzer/camera system common in the prior art is capable of monitoring the return system, however the system offers low resolution and is unstable inherently. It is spacious and takes up expensive head end real estate. The camera also requires periodic maintenance and frequent adjustments, especially if it shifts during operation. The spectrum analyzer/camera set up also is suspect to change as all spectrum analyzer controls are available to change without the knowledge of the field personnel viewing the screen. Lighting for the set up is another issue. Doors opening and closing, lights going on and off create dark, glaring or shadowed images which impact the reliability of the spectrum analyzer/camera set up. This prior art approach is clumsy and is accepted only in lieu of a better method. The present invention eliminates the spectrum analyzer camera duo.